1. Field of the Invention
The present invention relates to a dielectric ceramic composition, and in particular one that may be used for a ceramic capacitor for temperature compensation, for a resonator, and the like.
2. Description of the Prior Art
Ceramic capacitors for temperature compensation have heretofore been used for accomplishing tuning and resonance in a variety of electric devices. It has been desired to develop a capacitor which is small in size, has a small dielectric loss and has stable dielectric properties.
To meet the requirements for realizing a ceramic capacitor in a small size, the dielectric ceramic must have a large dielectric constant, a small dielectric loss (or, in other words, a large Q-value) and a small change in the dielectric constant despite a change in the temperature. In regard to reliability, the dielectric ceramic must be chemically stable, must have a large mechanical strength, and must have a large strength against thermal shock.
As the dielectric ceramic of this type, a material of the system of BaO--RE.sub.2 O.sub.3 --TiO.sub.2 (wherein RE.sub.2 O.sub.3 is an oxide of a rare earth element, the same holds hereinafter) has been extensively used. There has, for instance, been known a BaO--Nd.sub.2 O.sub.3 --TiO.sub.2 system material (see Japanese Patent Publication No. 20280/1975). The material of this system exhibits a dielectric constant of as large as about 55 to 95 and a temperature coefficient of capacitance TCC from -212 to +124 ppm/.degree.C.
There has further been known a BaO--(Nd.sub.2 O.sub.3 Sm.sub.2 O.sub.3)--TiO.sub.2 system material (Japanese Laid-Open Patent Publication No. 21010/1982) having a dielectric constant of from 50 to 95 and a TCC of from -400 to +900 ppm/.degree.C.
However, the BaO--RE.sub.2 O.sub.3 --TiO.sub.2 system material involves a problem in that it is difficult to confine the temperature coefficient of capacitance TCC from -30 to +30 ppm/.degree.C. and at the same time maintain a high dielectric constant. When it is attempted to confine the temperature coefficient of capacitance TCC from -30 to +30 ppm/.degree.C. yet maintain a high dielectric constant, the ceramic composition loses its sintering property. In order to stabilize the sintering property, therefore, a sintering aid such as SiO.sub.2 has heretofore been added. Such addition is accompanied, however, by problems such as a decrease in the dielectric constant .epsilon. r, deterioration in the temperature coefficient of capacitance TCC and loss of dielectric properties.